This invention relates to the field of orthopedic surgery in general, and more specifically to a joint prosthesis assembly and method for installing same.
A natural hip joint is a ball and socket joint in which a hemispherical head moves freely within a concave socket.
Artificial hip joints are an approximation of natural hip joints. More particularly, artificial hip joints consist of a metal (or metal alloy) head which articulates inside a metal (or metal alloy) cup. Often the metal socket is lined with very dense plastic, typically Ultra High Molecular Weight Polyethylene (UHMWPE), so as to reduce friction in the artificial bearing.
In 1994, 165,000 total hip replacements (THR""s) were performed in the United States. Due to the success of the THR operation, the improved quality of life it provides, and the increasing elderly population, this number is expected to increase in the future.
The expected life of an artificial hip is less than 10 years in active adults and about 10-20+ years in less active adults. When the artificial hip wears out, it must be replaced with a new artificial hip. This procedure is typically referred to as a xe2x80x9crevisionxe2x80x9d. In 1994, THR revision surgery accounted for approximately 20% of all THR surgery, and is expected to increase inasmuch as many patients are receiving THR""s at an earlier age. According to The National Center For Health Statistics, the annual number of total hip revisions will increase to 157,000 by the year 2010 and 219,000 by the year 2030.
THR revision surgery is typically more complex, time-consuming and complication-prone than standard THR surgery.
Accordingly, it is desirable to find a way to extend the life of the artificial hip.
According to the National Institutes of Health, xe2x80x9cthe principle cause of prosthesis failure appears to be the generation of particles, which, in turn, cause inflammation and bone resorption around the prosthesis (osteolysis)xe2x80x9d (NIH Consensus Statement: Total Hip Replacement. 1994; 12:1-31). The problem of osteolysis in THR involves three aspects: (a) the creation of debris particles within the artificial joints; (b) the migration of the debris particles to the bone around the prosthesis; and (c) a cellular reaction to the debris particles.
Extensive research has been published regarding the aforementioned first and third aspects of the problem.
More particularly, some current work is aimed at reducing the production of wear particles at the bearing surface of the artificial joint by using new metal-on-metal bearing designs, or modifying existing metal-polyethylene hips; however, it is unlikely that these modifications will eliminate wear particles completely, some of which have been found in the liver, spleen, and lymph nodes, and have been implicated as a cause of cancer.
Research aimed at reducing osteolysis by better understanding and controlling the biological cellular response, the third aspect described above, is widespread. Currently, a clinically useful approach has not been elucidated, although anti-inflammatory medications and anti-osteoclast medications show promise. Many investigators, however, have reservations about treating a localized problem with a systemic agent.
The present invention addresses the problem of osteolysis by focusing on the second aspect identified above, i.e., the migration of the debris particles to the bone around the prosthesis. More particularly, the present invention provides an improved xe2x80x9cSealed-Bearingxe2x80x9d total hip replacement (SB-THR) which incorporates the use of a limiting membrane that encapsulates the bearing and prevents debris particles from migrating from the prosthesis to the surrounding bone. The SB-THR could potentially eliminate osteolysis in the primary THR, thereby sparing thousands of patients from the ordeal of revision surgery and effecting significant savings in health care costs to society.
In addition, the SB-THR has the additional advantage that it can prevent so-called xe2x80x9cthird bodiesxe2x80x9d from entering the space between the femoral head and the pelvic socket, where they can accelerate wear on the head and the socket. Such xe2x80x9cthird bodiesxe2x80x9d typically comprise small pieces of bone which are created during the milling process when the femoral canal is prepared or the socket seat is prepared; and/or small pieces of the prosthesis which may flake off the outer surface of the prosthesis, e.g., hydroxyapetite or porous metal for encouraging bone ingrowth.
There has been some prior work in the area of the sealed-bearing concept. See, for example, U.S. Pat. Nos. 4,731,088 (Collier), U.S. Pat. No. 5,514,182 (Shea), and U.S. Pat. No. 5,755,807 (Anstaett et al.).
Accepting that the sealed bearing membrane is advantageous in eliminating or discouraging migration of debris particles, it becomes critical that the sealing membrane itself not present a problem, as by disconnection from a member of the joint.
A further complication lies in the fact that a sealing membrane in the hip joint flexes, when a leg is moved, not only in a bending direction, but also in a twisting or rotating direction, in which the sleeve-like membrane twists around its central axis.
There is, therefore, a need for a membrane adapted to encapsulate a bodily joint, such as a hip joint, so as to prevent migration of debris particles. There is further a need for securely attaching the membrane to the members of the joint. A related further need exists for effecting long term attachment of the membrane to the members of the joint, such that upon gradual elimination of holding power of the initial attachment means, other attachment means grow stronger and increase the holding security of the membrane. A still further need exists for compensating for the bend-and-twist movement of the membrane in hip assemblies, such that undue strain from repetitive movement does not weaken the structure of the membrane. And a still further need is to provide an improved total joint replacement assembly which may be used in joints other than the hip, e.g., the knee, the shoulder, the elbow, etc.
It is, therefore, an object of the invention to provide a sealed-bearing type of total hip replacement assembly and/or other total joint replacement assembly.
A further object of the invention is to provide such an assembly which includes an encapsulating membrane which captures and prevents migration of debris particles.
A further object of the invention is to provide such a membrane having thereon means for accurately and securely attaching the membrane to supporting structures at either end thereof.
A still further object of the invention is to provide such a membrane as permits localized ingrowth of tissue to further secure the membrane to the supporting structures.
A still further object of the invention is to provide such a membrane configured to reduce stress fatigue of the membrane resulting from long term use of the membrane.
A still further object of the invention is to provide a method for installing such an assembly.
With the above and other objects in view, as will hereinafter appear, a feature of the present invention is the provision of a joint prosthesis assembly, the assembly comprising a stem for disposition in a canal of a first bone constituting a first portion of the joint, a neck fixed to the stem, a collar fixed on the neck, the collar having a peripheral annular groove therein, and an articulating head fixed on the neck, the assembly further comprises a cup for disposition in a second bone constituting a second portion of the joint, and an insert disposed in the cup to provide an interior lining for the cup, the insert being adapted to receive the articulating head for movement therein, the insert having a peripheral annular groove therein. A sleeve-shaped membrane is provided with a first O-ring fixed thereto at a first end thereof for disposition in the insert groove, and a second C-ring fixed thereto at a second end thereof for disposition in the collar groove. The membrane is thereby disposed to capture particulate debris generated by the articulating head in the insert.
In accordance with a further feature of the invention, there is provided a joint prosthesis assembly comprising a stem for disposition in a canal of a first bone constituting a first portion of the joint, a neck fixed to the stem, a collar fixed on the neck, and an articulating head fixed on the neck. The assembly further comprises a cup for disposition in a second bone constituting a second portion of the joint, and an insert disposed in the cup to provide an interior lining for the cup, the insert being adapted to receive the articulating head for movement therein. A sleeve-shaped membrane is provided with a first connector structure fixed thereto at a first end thereof for connection to the insert, and a second connector structure fixed thereto at a second end thereof for connection to the collar. The membrane is thereby disposed to capture particulate debris generated by the articulating head in the insert. A first end portion of the membrane proximate the first end of the membrane and a second end portion of the membrane proximate the second end of the membrane have apertures therein permitting ingrowth of tissue to further secure the membrane in an operative position, and a middle portion of the membrane is devoid of apertures therein permitting ingrowth of tissue.
In accordance with a still further feature of the invention, there is provided a joint prosthesis assembly comprising a stem for disposition in a canal of a first bone constituting a first portion of the joint, a neck fixed to the stem, a collar fixed on the neck, and an articulating head fixed on the neck. The assembly further comprises a cup for disposition in a second bone constituting a second portion of the joint, and an insert disposed in the cup to provide an interior lining for the cup, the insert being adapted to receive the articulating head for movement therein. The assembly further includes a sleeve-shaped membrane having a first connector structure fixed thereto at a first end thereof for connection to the insert, and a second connector structure fixed thereto at a second end thereof for connection to the collar, the membrane being thereby disposed to capture particulate debris generated by the articulating head in the insert. The first and second ends are circularly displaced from each other around a central axis therethrough by an angle of about 35xc2x0-55xc2x0.
In accordance with still another feature of the invention, there is provided a joint prosthesis assembly comprising a stem for disposition in a canal of a first bone constituting a first portion of the joint, a neck fixed to the stem, a collar fixed on the neck, and an articulating head fixed on the neck. The assembly further includes a cup for disposition in a second bone constituting a second portion of the joint, and an insert disposed in the cup to provide an interior lining for the cup, the insert being adapted to receive the articulating head for movement therein. The assembly further comprises a sleeve-shaped membrane having a first connector structure fixed thereto at a first end thereof for connection to the insert, and a second connector structure fixed thereto at a second end thereof for connection to the collar. The membrane is thereby disposed to capture particulate debris generated by the articulating head in the insert. A middle portion of the membrane is formed so as to be pre-stressed in a circular direction around a central axis therethrough, by an angle of about 35xc2x0-55xc2x0.
In accordance with a still further feature of the invention, there is provided a method for installing a joint prosthesis assembly. The method comprises the steps of providing a joint prosthesis assembly comprising a stem for disposition in a canal of a first bone constituting a first portion of the joint, a neck fixed to the stem, a collar fixed on the neck, the collar having a peripheral annular groove therein, an articulating head fixed on the neck, a cup for disposition in a second bone constituting a second portion of the joint, an insert disposed in the cup to provide an interior lining for the cup, the insert being adapted to receive the articulating head for movement therein, the insert having a peripheral annular groove therein, and a sleeve-shaped membrane having a first O-ring fixed thereto at a first end thereof for disposition in the insert groove, and a second O-ring fixed thereto at a second end thereof for disposition in the collar groove. The method includes the further steps of mounting a first sub-assembly of the stem, neck, collar and articulating head on the first bone, mounting a second sub-assembly of the cup and insert on the second bone, mounting the membrane around the articulating head, fitting the articulating head in the insert, placing the first O-ring in the insert groove to fix the membrane first end to the insert, and placing the second O-ring in the collar groove to fix the membrane second end to the collar. The membrane is thereby disposed to capture particulate debris generated by the articulating head in the insert.
The above and other features of the invention, including various novel details of construction and combinations of parts, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular assembly and method embodying the invention are shown by way of illustration only and not as limitations of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.